The invention is concerned with a sprung vehicle seat which is adjustable for weight, so that the vehicle seat is always at the same preset height even when the occupants of the seat are of different weights, and which also permits the preset height to be adjusted.
Such a seat may comprise a gas spring which is disposed between a seat support frame carrying the upholstery or cushion or the like and a main or base frame, a switching means for controlling the gas spring and an actuator member which is displaced relative to the switching means when there is a change in the height of the seat support frame above the main frame. The seat may further comprise a slide member which can be fixed to one of the seat support and main frames, for the purposes of height adjustment, selectively in a plurality of positions on a line of displacement which is parallel to the relative displacement between the switching means and the actuator member, and a holder which is movable on the slide member transversely with respect to the line of displacemnt thereof between a first and a second position and which carries either the switching means or the actuator member. In the first position of the holder, into which it is spring-biassed, the actuator member and the switching means are spaced from each other in a direction transverse with respect to their relative movement by a spacing such that the actuator member and the switching means do not come into co-operation with each other in the event of normal spring movements of the seat, in order to avoid unnecessary actuation of the gas spring, while in the second position of the holder, the actuator member and the switching means are sufficiently close together in a direction transverse to their relative movement that they co-operate for the purposes of adjustment for weight. The seat further comprises a three-stage or three-phase actuating means which includes at least one pivotal actuating lever and which, in the first actuating phase or stage, pivots the holder into its second position, in the subsequent second actuating stage it releases the locking on the slide member, and in a third actuating stage, it shifts the slider from one position into another.
A vehicle seat of the above-indicated general kind can be used in particular on tractors, but it can also be employed for other vehicles.
DAS (German published application) No. 15 05 507 describes a vehicle seat of the above-indicated general kind, in which the lower end of the slide member is guided vertically on the main frame and the upper end of the slide member can be engaged with a row of detent positions on the seat support frame. The actuator member is provided on the holder, and the switching means for controlling the gas spring is stationarily secured to the main frame.
For the purposes of engaging the slide member with the substantially vertical row of detent positions on the seat support frame, the arrangement has a transverse pin member which is fixed to the upper end of the slide member and which can be brought into engagement with the detent assembly. The slide member is pivotal at its lower, vertically guided end, about an axis which is parallel to the above-mentioned upper transverse pin member. A rod which is pivotally connected to the pin member and which extends normal thereto engages into a tube member which is rotatable transversely to the longitudinal direction of the rod, and is biassed towards the detent arrangement by a spring disposed in the tube member, so that the transverse pin member is urged into detent engagement. A crank which is pivotal separately about the axis of rotation of the tube member is connected to the transverse pin member by way of a connecting rod. The arrangement has a pivotal actuating lever for pivoting the tube member, and a pivotal actuating lever for rotating the crank, while the actuating lever for the crank engages upon pivotal movement into a recess in the actuating lever to produce pivotal movement of the tube member.
The mode of operation in regard to actuation of the above-discussed vehicle seat is as follows:
In a first actuating phase, the actuating lever, which is rigidly connected to the crank, is pivoted so that the transverse pin member of the slide member is displaced outwardly, but without leaving the detent means. Due to the slight pivotal movement of the slide member which occurs as a result, the holder, which is in the form of a double-armed lever and which bears with one end against the tube member acting as an abutment, is pivoted in such a way that the actuator member co-operates with the switching means. Adjustment for weight is then effected.
In the second phase of actuation, the actuating lever, which is rigidly connected to the crank, must be pivoted even further until it reaches the recess in the actuating lever which is associated with the tube member. When this occurs, the transverse pin member of the slide member is taken completely out of the detent positions so that the lock between the slide member and the frame is now released.
In the third phase of actuation, both actuating levers are jointly pivoted in one direction or the other so that the transverse pin member moves along a short circular path, beyond the row of detent positions. However, the path of movement can be considered as being substantially straight. Upon release of the actuating lever, which is connected to the crank and which is disposed in the recess of the lever connected to the tube member, the slide member together with the transverse pin member is pivoted towards the row of detent positions by virtue of the force of the spring in the tube member, and the slide member comes into detent engagement with the detent arrangement, at a fresh position.
It has been found that the above-discussed arrangement suffers from the disadvantage that it has two actuating levers which confuse the user of a seat who has not previously had the mode of operation of the two levers explained to him, so that the user of the seat cannot properly operate the seat straightaway. In addition, actuating two levers in a given sequence is a complicated operation.
It has also been found that the above-discussed arrangement suffers from the disadvantage that the transition from the first phase of actuation, in which adjustment for weight is effected and the transverse pin member of the slide member is still engaged with the detent arrangement, to the second actuating phase, in which the interlock between the slide member and the detent arrangement is to be released, is a fluid situation. In many cases, an unskilled occupant of the seat will pivot the lever connected to the crank to an excessive degree so that the transverse pin member of the slide member comes out of engagement with the detent arrangement and it is not possible to make an adjustment for weight, with a fixed height of seat. The fluid transition between the first phase of actuation and the second phase of actuation at least increases the difficulty involved in operating the seat.